LONG-TERM OBJECTIVE: To gain insight into the cellular and dynamic mechanisms and functional roles of neural feedback loops for visual processing. SPECIFIC AIMS: The aim is to provide an understanding of the dynamic and neural mechanisms of feedback for visual processing. Here the avian isthmo-tectal feedback loop serves as an experimentally accessible model preparation for neural feedback systems in general. The specific aims are (1) to determine the cellular and synaptic properties in the isthmo-tectal circuitry and (2) to identify the role of isthmo-tectal system parameters for signal processing. The proposed research will provide fundamental insight into the mechanisms and the functional roles of feedback loops in central nervous systems. RESEARCH DESIGN AND METHODS: Neural feedback loops are critical for information processing in all vertebrates, but cellular mechanisms of feedback have been difficult to investigate in mammals because of anatomical limitations. The anatomical organization of the avian isthmotectal loops provides two major advantages for the study of feedback mechanisms in neural processing: The isthmo-tectal feedback loop is largely intact and accessible in the chick midbrain slice preparation, which we have developed. The two isthmic nuclei interact exclusively with the tectum but are otherwise isolated from the rest of the brain. We will approach our objective by studying cellular mechanisms of isthmo-tectal feedback in the slice preparation and by interpreting the functional roles of these mechanisms for visual processing in experimentally constrained model simulations. The feature that makes feedback approachable in the isthmo-tectal system is that we can study modulatory interneurons in a complex self contained system, yet these interneurons are physically separate from and exclusively connected to the system that they modulate. HEALTH-RELATEDNESS: The understanding of the dynamic and neural mechanisms of feedback for visual processing provides the basis for the pharmacological and prosthetic intervention of visual perceptual impairments. ARRA-RELATEDNESS: A total of six neuroscience jobs will be created and retained through this project.